Wing is a general term applied to a surface designed to develop lift. The cordwise cross-section of the wing is an airfoil shape. The plan form of the wing may be rectangular, triangular, trapezoidal, elliptical or a combination of a rectangular root section with a trapezoidal or rounded tip sections. Generally, the plan form of the wing is trapezoidal with slightly rounded tips for subsonic designs and triangular for transonic and supersonic designs in order to obtain a sweep back angle equal to or greater than the mach angle.
Generally, the wing is composed of a surface, of members supporting that surface in the external shape of the desired airfoil, and of an underlying structural framework to support the members. The structural framework conveys lift to the fuselage of an aircraft. Typically, the structural framework is defined by one or more spars and ribs fastened to the spars at intervals along the length of the spars.
Spars can be constructed of wood or metal. Usually wood is preferred for small or medium sized airplanes, whereas metal in the form of drawn or extruded shapes, tubes, corrugations, is used for the built-up spars of larger airplanes. Built-up spars are constructed with several members fastened together, for example, by riveting. In many aircraft applications it is preferred to seal the several members of the built-up spar relative to one another.